Semiconductor light emitting devices, such as Light Emitting Diodes (LEDs) or laser diodes, are widely used for many applications. As is well known to those having skill in the art, a semiconductor light emitting device includes a semiconductor light emitting element having one or more semiconductor layers that are configured to emit coherent and/or incoherent light upon energization thereof. In particular, a light emitting diode or laser diode, generally includes an active region on a microelectronic substrate. The microelectronic substrate may be, for example, gallium arsenide, gallium phosphide, alloys thereof, silicon carbide and/or sapphire. Continued developments in LEDs have resulted in highly efficient and mechanically robust light sources that can cover the visible spectrum and beyond. These attributes, coupled with the potentially long service life of solid state devices, may enable a variety of new display applications, and may place LEDs in a position to compete with the well entrenched incandescent and fluorescent lamps. Recently, applications for LEDs emitting in the deep UV (DUV) region of the spectrum (less than roughly 375 nm) have been identified. These applications include chemical and biological agent detection systems, non-line-of-site communication systems, water and air purification systems and/or tanning applications.
Much development interest and commercial activity recently has focused on LEDs that are fabricated in or on silicon carbide, because these LEDs can emit radiation in the blue/green portions of the visible spectrum. See, for example, U.S. Pat. No. 5,416,342 to Edmond et al., entitled BLUE LIGHT-EMITTING DIODE WITH HIGH EXTERNAL QUANTUM EFFICIENCY, assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. There also has been much interest in LEDs that include gallium nitride-based diode regions on silicon carbide substrates, because these devices also may emit light with high efficiency. See, for example, U.S. Pat. No. 6,177,688 to Linthicum et al., entitled PENDEOEPITAXIAL GALLIUM NITRIDE SEMICONDUCTOR LAYERS ON SILICON CARBIDE SUBSTRATES, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
Ultraviolet light emitting devices have also been described, for example, in U.S. Pat. No. 6,734,033 to Emerson et al. entitled ULTRAVIOLET LIGHT EMITTING DIODE; U.S. Pat. No. 6,664,560 to Emerson et al. entitled ULTRAVIOLET LIGHT EMITTING DIODE; U.S. Pat. No. 5,661,074 to Tischler entitled HIGH BRIGHTNESS ELECTROLUMINESCENT DEVICE EMITTING IN THE GREEN TO ULTRAVIOLET SPECTRUM AND METHOD OF MAKING THE SAME; U.S. Pat. No. 5,874,747 to Redwing et al. entitled HIGH BRIGHTNESS ELECTROLUMINESCENT DEVICE EMITTING IN THE GREEN TO ULTRAVIOLET SPECTRUM AND METHOD OF MAKING THE SAME; and U.S. Pat. No. 5,585,648 to Tischler entitled HIGH BRIGHTNESS ELECTROLUMINESCENT DEVICE, EMITTING IN THE GREEN TO ULTRAVIOLET SPECTRUM, AND METHOD OF MAKING THE SAME, the disclosures of which are incorporated herein as if set forth fully herein.
Others have produced relatively high efficiency LEDs in the DUV region of the spectrum. For example, Nichia Corporation has announced the development of light emitting diodes having outputs of 365 nm and 375 nm. See Nichia product specifications, NSHU550A, NSHU590A, NSHU550B and NSHU590B. However, to date high efficiency DUV LEDs with emission wavelengths less than approximately 360 nm have not been achieved due to several fundamental technical challenges including the following: output power too low for a given drive current, wallplug efficiency too low, and device lifetime too low.